Method and apparatus for optimizing power consumption of a terminal in a mobile communication system

ABSTRACT

The present invention relates to a method and to an apparatus for optimizing the power consumption of a terminal in a mobile communication system. The method for optimizing power consumption of a terminal in a mobile communication system comprises: a determination step of determining whether there is a need for changing a configuration for a discontinuous reception operation of the terminal; and a transmission step of transmitting, to a base station, a request message for a change in the discontinuous reception operation, if it is determined that the change is needed.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/814,373 filed Jul. 30, 2015, which is a continuation of U.S.patent application Ser. No. 13/885,652 filed May 15, 2013, which isrelated to and claims priority under 35 U.S.C. §365 to InternationalPatent Application No. PCT/KR2011/008707 filed Nov. 15, 2011, entitled“METHOD AND APPARATUS FOR OPTIMIZING POWER CONSUMPTION OF A TERMINAL INA MOBILE COMMUNICATION SYSTEM”. International Patent Application No.PCT/KR2011/008707 claims priority under 35 U.S.C. §365 and/or 35 U.S.C.§119(a) to U.S. Provisional Application No. 61/413,914 filed Nov. 15,2010 and 61/484,645 filed May 10, 2011 all of which are incorporatedherein by reference into the present disclosure as if fully set forthherein.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a mobile communication system and, inparticular, to a method and apparatus for optimizing power consumptionof a terminal in the mobile communication system.

Description of the Related Art

Typically, the mobile communication system has been developed for theuser to communicate on the move. With the rapid advance of technologies,the mobile communication system has evolved to the level capable ofproviding high speed data communication service as well as voicecommunication service.

Recently, as one of the next generation mobile communication system,Long Term Evolution (LTE) is on the standardization by the 3^(rd)Generation Partnership Project (3GPP). LTE is a technology designed toprovide high speed packet-based communication of up to 100 Mbps and aimsat commercial deployment around 2010 timeframe. In order to accomplishthe aim, a discussion is being held on several schemes: one scheme forreducing the number of nodes located in a communication path bysimplifying a configuration of the network, and another scheme formaximally approximating wireless protocols to wireless channels.

Meanwhile, unlike voice service, the data service is provided on theresource determined according to the data amount to be transmitted andchannel condition. Accordingly, the wireless communication system,especially cellular communication, is provided with a scheduler managestransmission resource allocation in consideration of the requiredresource amount, channel condition, data amount, etc. This is the factin the LTE system as the next generation mobile communication system,and the scheduler located at the base station manages the transmissionresource allocation.

More recently, discussions are focused on LTE-advanced (LTE-A) evolvedfrom LTE with the adaptation of various novel techniques. In Release 11,Diverse Data Application (DDA) has been introduces as a part of WorkItem (WI) for reducing power consumption of the terminal. In associationwith the WI, various studies are being conducted in order to optimizethe power consumption of the terminal.

DISCLOSURE OF INVENTION Technical Problem

The present invention proposes a method for optimizing the powerconsumption of a terminal, and it is an object of the present inventionto provide a method and apparatus for changing discontinuous receptionoperation settings efficiently according to the traffic properties inthe radio communication system supporting various data traffics so as tooptimize the power consumption of the terminal.

Solution to Problem

In order to solve the above problem, a power consumption optimizationmethod of a terminal in a mobile communication system includesdetermining whether a discontinuous reception configuration of theterminal is necessary to be changed; and transmitting, when necessary tobe changed, a discontinuous reception configuration change requestmessage to a base station.

Also, a terminal for optimizing power consumption in a mobilecommunication system includes a transceiver which transmits and receivesdata or control signals to and from a base station; and a controllerwhich controls determining whether a discontinuous receptionconfiguration of the terminal is necessary to be changed andtransmitting, when necessary to be changed, a discontinuous receptionconfiguration change request message to a base station.

Advantageous Effects

According to the present invention, in the radio communication systemsupporting various data traffics, it is possible to change the DRXconfiguration efficiently so as to optimize power consumption of theterminal according to the traffic property.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart illustrating the DRX operation procedure of theterminal.

FIG. 2 is a diagram illustrating an enhanced DRX method for reducing thepower consumption of the terminal according to an embodiment of thepresent invention.

FIG. 3 is a flowchart illustrating detailed operation procedure of thefirst embodiment of the present invention.

FIG. 4 is a signal flow diagram illustrating the power consumptionmethod of the terminal according to the second embodiment of the presentinvention.

FIG. 5 is a signal flow diagram illustrating the operation procedure ofthe third embodiment.

FIG. 6 is a block diagram illustrating the configuration of the terminalaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In the LTE system, Discontinuous Reception (DRX) is adopted to minimizepower consumption of the terminal. The terminal usually has to monitorthe channel to detect the data addressed to it. However, if the usermonitors the channel always, this causes significant power consumption.Accordingly, there is a room for reducing the power consumption of theUE in such a way that the terminal monitors the channel to detect datafor predetermined duration. This is referred to as DRX, and FIG. 1 showsa DRX operation procedure.

FIG. 1 is a flowchart illustrating the DRX operation procedure of theterminal.

Part (a) of FIG. 1 shows the operation of the terminal in the case of noreceipt of data. The terminal monitors Physical Downlink Control Channel(PDCCH) as a downlink control channel only in duration occurringperiodically but not always. This period is referred to as DRX cycle100, and the PDCCH monitoring is limited to the DRX cycle using anon-duration timer 105. That is, the on-duration timer starts at everyDRX cycle such that the terminal monitors PDCCH until the time expires.

In this case, the DRX cycle and the on-duration timer value is notifiedto the terminal through a dedicated Radio Resource Control (RRC)message. The base station knows the DRX cycle and on-duration timervalue of each terminal and, if data addressed a certain terminal, sendsthe scheduling information for the corresponding terminal on PDCCH forthe time duration of on-duration timer. If PDCCH carries the schedulinginformation addressed to one terminal, DRX operates for the terminal toexpand the time for monitoring the channel with multiple timers.

Part (b) of FIG. 1 shows the DRX operation in the case that newscheduling information is carried on PDCCH. If the schedulinginformation for the corresponding terminal is carried on PDCCH for theon-duration of the terminal as denoted by reference number 110, theterminal starts the DRX inactivity timer 115 and retransmission timer(HARQ RTT timer) 120. The active time of the terminal is expanded in theduration while the DRX inactivity timer is running. That is, while theDRX inactivity timer is running, the terminal continues monitoringPDCCH. If not scheduling information is carried on PDCCH, the HARQ RTTtime starts. There is no need for the terminal to monitor the PDCCHbefore receiving new scheduling information for retransmission aftertransmitting a NACK corresponding to the data transmitted by the basestation. Accordingly, the terminal refrains from monitoring PDCCH forthe duration while the HARQ RTT timer is active. That is, the HARQ RTTtimer value is determined in consideration of the Round Trip Time inHARQ operation. However, the other timers, i.e. DRX inactivity timer andon-duration timer are running, the terminal stays in active statealthough the HARQ RTT timer is active.

If the HARQ RTT timer has expired and the soft buffer data have not beendecoded successfully, the DRX retransmission timer 125 starts. If thecorresponding DRX retransmission timer starts, the terminal stays inactive state. If scheduling information is received again before theexpire of the DRX retransmission timer as denoted by reference number130, the terminal starts HARQ RTT timer and stops the currently runningDRX retransmission timer as denoted by reference number 135. Since theDRX inactivity timer stops as denoted by reference number 140 and onlythe HARQ RTT timer is running, the terminal leaves the active state. Ifthe HARQ RTT timer expires without decoding the data successfully, theDRX retransmission timer starts as denoted by reference number 145. Ifscheduling information arrives before the expiry of the DRXretransmission timer as denoted by reference number 150, the HARQ RTTtimer starts and the DRX retransmission timer stops as denoted byreference number 155. If the data in the soft buffer are decodedsuccessfully as denoted by reference number 175, the currently runningHARQ RTT timer stops.

Meanwhile, although DRX make it possible to reduce power consumption ofthe terminal, there is a room for reducing the power consumption moreefficiently by adjusting the DRX operation and configuration valuesdynamically. By taking notice of this, the present invention proposes amethod for reducing the power consumption efficiently.

FIG. 2 is a diagram illustrating an enhanced DRX method for reducing thepower consumption of the terminal according to an embodiment of thepresent invention.

First, the terminal receives scheduling information from the basestation as denoted by reference number 200. If it is determined thatthere is no more data to be transmitted/received as denoted by referencenumber 205, the terminal stops the DRX inactivity timer, which hasstarted at the timing 200, before expiry and configure the next DRXcycle to be longer as denoted by reference number 125 or applyingshorter on-duration as denoted by reference number 220 to reduce powerconsumption further.

In order to accomplish this operation, there is a need of a mechanismfor the terminal to notify the base station of the current terminaltraffic condition and unavailability of the current DRX configuration.Also, there is a need of a mechanism for transmitting DRX configurationfor more power conservation to the terminal efficiently. The presentinvention proposes such mechanisms.

The conventional DRX configuration can be classified into one of twolevels depending on the situation. That is, the two configurations ofshort DRX and long DRX are sent to the terminal through RRC connectionreconfiguration message in advance. The long DRX has the DRX cyclelonger than that of the short DRX while the timer-related configurationvalues are not differentiated between the long and short DRXs. Thedefault configuration is the long DRX and, if the short DRX is required,the short DRX is triggered with Media Access Control (MAC) CE. The shortDRX is changed for the long DRX automatically after being applied forpredetermined time duration.

Accordingly, by taking notice of the power conservation mode, it is notappropriate for applying the conventional DRX configuration from variousviewpoints.

In order to enhance the power conservation effect, it is necessary toadjust the DRX inactivity timer and on-duration timer depending on thesituation as wells as the DRX cycle as described above.

The conventional DRX mechanism allows the base station to trigger thechange from the long DRX to the short DRX, but the change from the shortDRX to the long DRX depends on a timer. In order to save power, however,it should be allowed for switching the short DRX to the long DRX or alonger DRX for more power saving at a wanted time.

Finally, the conventional DRX mechanism depends on the determination ofthe base station without input from the terminal in switching betweenthe DRX configurations. However, there is a need of the data trafficcondition of the terminal in order to accomplish the efficient poserconservation effect.

Descriptions are made of the methods for reducing power consumptionaccording to the first to third embodiments of the present inventionhereinafter. In the first embodiment, a description is made of themethod for triggering an RRC message, i.e. DRX configuration changerequest message, transmitted from a terminal to a base station. In thesecond and third embodiments, descriptions are made of the methods fordetermining DRX configuration value minimizing power consumption andrequesting for changing DRX configuration. The second and thirdembodiments are similar to each other with the exception in theprocedure of transmitting the DRX configuration change request messageto the base station.

First Embodiment

In the first embodiment of the present invention, a description is madeof the method for the terminal to trigger a RRC message requesting forchange of DRX, i.e. DRX configuration change request message, to betransmitted to the base station.

FIG. 3 is a flowchart illustrating detailed operation procedure of thefirst embodiment of the present invention.

First, the terminal receives, from a higher layer, a report informingthat there is no more data to be transmitted to the base station at step300. The terminal determines whether DRX configuration change isnecessary for reduction of power consumption based on a few conditionsat step 305. For example, the following three conditions may beconsidered.

-   -   The length of on-duration is longer than a predetermined        threshold value?    -   The long DRX cycle is shorter than a predetermined threshold        value?    -   The DRX inactivity length is longer than a predetermined        threshold?

If at least one of the three conditions is not fulfilled, it isdetermined that DRX change is necessary for reducing power consumption.In this case, the terminal triggers an RRC control message, i.e. DRXconfiguration change request message at step 310. An indicatorindicating that there is no more data to be transmitted by the terminalis included in the RRC control message at step 315.

Next, the terminal sends the base station the DRX configuration requestmessage at step 320.

Meanwhile, if a handover command is received before the receipt of a DRXconfiguration change response message (RLC ACK) corresponding to the RRCmessage at step 325, the terminal performs step 305 again in a new cell.Otherwise, if the DRX configuration change response message is receivedfrom the base station, the terminal ends the DRX configuration requestprocedure.

Second Embodiment

In the second embodiment of the present invention, a description is madeof the method for determining DRX configuration value for powerconsumption minimization and requesting change of the DRX configuration.Particularly, a Signaling Connection Release Indication (SCRI) messagetransmitted by the terminal is delivered through an uplink data channel(e.g. MAC CE). The SCRI message is used to request for change of the DRXconfiguration value for minimizing power consumption when there is nomore data to be transmitted by the terminal. In the followingdescription, the term ‘SCRI’ is interchangeable used with the term ‘DRXconfiguration change request message.”

FIG. 4 is a signal flow diagram illustrating the power consumptionmethod of the terminal according to the second embodiment of the presentinvention.

The base station 405 sets a DRX configuration value for minimizing thepower consumption of the terminal at step 410. This is to define a DRXconfiguration for power conservation with DRX inactivity timer, DRXcycle, and on-duration timer in the range of values tolerable in thesystem, and this is referred to as Power Serving Set in an embodiment ofthe present invention. For example, the Power Serving Set may beprovided with the shortest DRX inactivity timer value, longest DRX cyclevalue, and shortest on-duration timer value capable of being provided inthe system.

Next, the base station sends the terminal 400 the Power Saving Set usingthe dedicated RRC message, i.e. RRC connection reconfiguration message,at step 415. In response to the Power Saving Set, the terminal sends thebase station an RRC connection reconfiguration complete message at step420.

The terminal and the base station communicate data to each other at step425. If there is no more data to transmit at step 430, the terminalcompares the current DRX configuration value with the Power Serving Setvalue received previously from the base station at step 435.

If at least one currently configured DRX configuration values, i.e. DRXinactivity timer value, DRX cycle value, and on-duration timer value,mismatch the Power Saving Set, the terminal determines that it isnecessary to adjust the current DRX configuration value. At this time,the terminal sends the base station a DRX configuration change requestmessage (i.e. SCRI message) at step 440. The DRX configuration changerequest message (SCRI) transmission condition is fulfilled when theterminal has no more data to be transmitted and when it is necessary tocompare the previous Power Saving Set and the current DRX configurationor the more efficient DRX configuration is required as compared to thecurrent DRX configuration. Also, the DRX configuration change requestmessage may be transmitted when the terminal is not scheduled for apredetermined time.

With the transmission of the DRX configuration change request message(SCRI message), an SCRI timer starts. The SCRI timer may be used as DRXconfiguration change request message retransmission condition.

Upon receipt of the DRX configuration change request message (SCRI), thebase station determines that the terminal's DRX configuration values arerequired to be changed to the Power Saving Set values at step 450.Accordingly, the base station sends the terminal a DRX configurationchange response message indicating change of the DRX configurationvalues to the power saving set in the MAC CE at step 455. In order toaccomplish this, a new MAC CE has to be defined. Also, it is necessaryto define a new SCID to identify the new MAC CE.

Upon receipt of the DRX configuration change response message from thebase station, the terminal sets the terminal's DRX configuration valuesto the Power Saving Set values, at step 460, using the Power Saving Setconfiguration information received from the base station previously.

Meanwhile, the terminal may not receive the DRX configuration changeresponse message from the base station at step 465 until the timerstarted at step 445 expires. If the terminal is not configured with thePower Saving Set before the expiry of the timer, the terminalretransmits the DRX configuration change request message (SCRI) to thebase station at step 470. At this time, the corresponding timer restartsat step 475.

In this way, the DRX configuration change request message (SCRI)retransmission is determined based on the timer. That is, if it fails tochange for the Power Saving Set until the timer expires, the SCRI isretransmitted. If it is determined to refrain from change at step 480,the base station sends the terminal a MAC CE indicating the related DRXcommand at step 485. Here, it is possible to stop the timer or restartthe timer at step 490. If the timer expires again at step 495, theterminal may retransmit the SCRI message. As the SCRI retransmissioncondition, the timer stops or restarts when scheduling information isreceived or when SR occurs. If the scheduling information is received orSR occurs, the SCRI message transmission is suspended because it isinappropriate to configure with the power saving set.

Third Embodiment

In the third embodiment of the present invention, a description is madeof the method for determining DRX configuration value for powerconsumption minimization and requesting change of the DRX configuration.The third embodiment is similar to the second embodiment with theexception that the Signaling Connection Release Indication (SCRI)transmitted by the terminal is delivered in a control message, i.e. RRCmessage. In the following description, the term ‘SCRI’ isinterchangeable used with the term ‘DRX configuration change requestmessage.”

FIG. 5 is a signal flow diagram illustrating the operation procedure ofthe third embodiment.

Steps 510 to 545 of FIG. 5 are identical with steps 410 to 445 of FIG.4. If it is determined that the terminal's Power Saving Set is necessaryto be changed at step 550, the base station sends the terminal adedicated RRC message, i.e. RRC connection Reconfiguration(RRCConnectionReconfiguration) message at step 555. The RRC connectionReconfiguration (RRCConnectionReconfiguration) may include only theindicator indicating to change the terminal's DRX configuration valuesfor the power saving set values store in the terminal previously ornewly configure DRX configuration information. The RRC ConnectionReconfiguration message may make it possible for the base station toperform control flexibly in adaptation to the situation.

FIG. 6 is a block diagram illustrating the configuration of the terminalaccording to an embodiment of the present invention.

The terminal includes a transceiver 650, a DRX calculator 615, acontroller 610, a multiplexer/demultiplexer 620, a control messageprocessor 635, and various higher layer devices 635 and 630.

The transceiver 650 receives data and predetermined control signals ondownlink carriers and transmits data and predetermined control signalson uplink carriers.

The control unit 610 controls overall operations for optimizing powerconsumption of the terminal and signal flows among the function blocks.

In more detail, the control unit 610 instructs themultiplexer/demultiplexer 620 to generate MAC PDU according to thecontrol signal, i.e. the scheduling information indicated in the uplinkgrant, provided by the transceiver 650. The control unit determineswhether to change DRX configuration and, if it is necessary to changeDRX configuration, instructs the optimal DRX calculator 615 to calculateoptimal DRX configuration value. Whether to change DRX is determinedbased on the SCRI message sent by the control message processor 635. Thecontrol unit 610 controls the multiplexer/demultiplexer 620 such thatthe scheduling information is transmitted according to the DRX cycle.The control unit 610 transmits the optimal DRX configuration valueprovided by the DRX calculator 615 to the multiplexer/demultiplexer. Theoptimal DRX calculator 615 calculates the optimal DRX configurationvalue and sends it to the controller 610 under the control of thecontroller 610. The DRX configuration value is processed so as to betransmitted to the terminal by means of the control message processor635.

The multiplexer/demultiplexer 620 multiplexes the data generated by thehigher layer device 625 and the control message processor 635 ordemultiplexes the data received by means of the transceiver to deliverthe demultiplexed data to appropriate higher layer device 625 or thecontrol message processor 635.

The control message processor 630 processes the control messagetransmitted by the network and takes a necessary action. For example,the control message processor 635 may send the PHR parameter containedin the control message to the controller 610 or send the newly activatedcarriers information to the transceiver 605 such that the transceiver isconfigured with the carriers. The higher layer device 625 may beestablished per service and process the data generated by user servicesuch as FTP or VoIP to the multiplexer or process the data from thedemultiplexer 620 to the higher layer service application.

Although the description is directed to the case where the terminalconsists of separate blocks responsible for different functions, this isjust an example but not limited to the separated function blockconfiguration. For example, the controller 610 may perform all theabove-described functions by itself.

In detail, the controller 610 may determine that it is necessary tochange DRX configuration of the terminal and control to transmit a DRXconfiguration change request message to the base station.

In this case, according to the first embodiment of the presentinvention, if the length of on duration is long than a predeterminedthreshold, if the long DRX cycle is shorter than a predeterminedthreshold, or if the DRX inactivity length is longer than apredetermined threshold, the controller 610 determines that there is aneed of changing the DRX configuration. The DRX configuration changerequest message may include an indicator indicating that the terminalhas no more data to transmit.

Meanwhile, in the first embodiment of the present invention, a handovercommand is received before receiving the ACK message corresponding tothe DRX configuration change request message from the base station, thecontrol unit may perform handover to determine whether the DRX configurehas to be changed in the new cell.

In the case of the second embodiment of the present invention, thecontrol unit 610 may control to receive a Power Saving Set including atleast one DRX configuration value from the base station. The PowerSaving Set may include at least one of a DRX inactivity timer value, aDRX cycle value, and an on-duration timer value.

In the case that there is no data to be transmitted to the base station,the control unit 610 may compare the current DRX configuration valuewith the configuration value contained in the Power Saving Set. If atleast one configuration value mismatch, the control unit 610 may triggertransmission of DRX configuration change request message to the basestation.

In this case, the DRX configuration change request message istransmitted to the base station in a MAC CE through a data channel inthe second embodiment and in an RRC message through a control channel.

If a DRX configuration change response message is received from the basestation, the control unit 610 controls to change the DRX configurationvalue of the terminal with the configuration information of the PowerSaving Set carried in the message.

What is claimed is:
 1. A method for providing preferred powerinformation by a base station in a wireless communication system, themethod comprising: generating information that indicates to providepreferred power information of a terminal; transmitting, to theterminal, the information via radio resource control (RRC) signaling;receiving, from the terminal, a message if current preferred powerinformation is different from previous preferred power information and atimer is not running, wherein the message includes preferred powerinformation.
 2. The method of claim 1, wherein the timer starts orrestarts if the message is received.
 3. The method of claim 1, whereinthe receiving of the message is performed if the terminal has no data tobe transmitted.
 4. The method of claim 1, wherein the power informationincludes at least one of a predetermined discontinuous receptioninactivity timer value, a discontinuous reception cycle value, and anon-duration timer value.
 5. The method of claim 1, wherein the basestation is connected to the terminal by a hand over.
 6. The method ofclaim 1, further comprising: transmitting a response message of themessage to the terminal, wherein the response message includes powerinformation for changing a power saving configuration of the terminal.7. The method of claim 1, wherein receiving the message from theterminal comprises receiving the message from the terminal on a datachannel.
 8. A base station for providing preferred power information ina wireless communication system, the base station comprising: atransceiver configured to transmit and receive a signal; and acontroller configured to control: generating information that indicatesto provide preferred power information of a terminal; transmitting, tothe terminal, the information via radio resource control (RRC)signaling; and receiving, from the terminal, a message if currentpreferred power information is different from previous preferred powerinformation and a timer is not running, wherein the message includespreferred power information.
 9. The base station of claim 8, wherein thetimer starts or restarts if the message is received.
 10. The basestation of claim 8, wherein the receiving of the message is performed ifthe terminal has no data to be transmitted.
 11. The base station ofclaim 8, wherein the power information comprises at least one of apredetermined discontinuous reception inactivity timer value, adiscontinuous reception cycle value, and an on-duration timer value. 12.The base station of claim 8, wherein the base station is connected tothe terminal by a hand over.
 13. The base station of claim 8, whereinthe controller is further configured to control a transmission of aresponse message of the message to the terminal, wherein the responsemessage includes power information for changing a power savingconfiguration of the terminal.
 14. The base station of claim 8, whereinthe controller is configured to receive the message from the terminal ona data channel.